The formation of new blood vessels by angiogenesis is a central event in many different pathological states, including ocular diseases causing blindness, such as macular degeneration, diabetic retinopathy and states of retinal hypoxia, states of chronic inflammation, such as rheumatoid arthritis, in psoriasis, atherosclerosis, restenosis, as well as in cancer growth and metastasis. In addition, hemangioma is caused by uncontrolled proliferation of endothelial cells. Given that many of these diseases are of a chronic nature and presently lack satisfactory cure, search for treatments and drugs against these diseases is very important. According to current paradigm all solid tumors need to induce angiogenesis to cover their metabolic needs and grow over millimeter size. Therefore a possibility to inhibit tumor growth by reducing the neovascularization within tumor tissue would be most useful as adjuvant therapy for cancer cure. To this end, an agent blocking angiogenesis has the potential to constitute a medicament for all these common angiogenesis- (and/or endothelial cell-) dependent diseases.
One interesting target for drugs against diseases of this kind has been CD44 (Naot et al., Adv Cancer Res 1997; 71 :241-319). CD44 is a cell surface receptor for the large glycosaminoglycan of the extracellular matrix hyaluronic acid (HA) (Aruffo et al., Cell 1990; 61:1303-13). CD44 plays a role in various cellular and physiological functions, including adhesion to and migration on HA, HA degradation and tumor metastasis. The CD44 receptor shows a complex pattern of alternative splicing in its variable region of the extracellular domain (Screaton et al., PNAS 1992; 89: 12160-4). CD44 is able to bind matrix metalloproteinase-9 (MMP-9) and can thereby localize MMP-9 to the cellular membrane, which may in part explain its activity in promoting tumor cell invasion and metastasis (Yu, 1999).
Among patent references disclosing CD44 and its connection to diseases described above may U.S. Pat. Nos. 6,025,138, 5,902,795, 6,150,162, 6,001,356, 5,990,299 and U.S. Pat. No. 5,951,982 be mentioned.
WO94/09811 describes the use of CD44 in treating inflammation or detecting cancer metastasis of hematopoietic origin. Use of CD44 for inhibiting solid tumor growth or angiogenesis is not disclosed. WO 99/45942 discloses the use of HA-binding proteins and peptides including CD44 to inhibit cancer and angiogenesis-dependent diseases. CD44 is mentioned as one example of a long list of HA-binding proteins. In both publications the use of CD44 is limited to its ability to bind hyaluronic acid.
Ahrens et al. (Oncogene 2001; 20; 3399-3408) discloses that soluble CD44 inhibits melanoma tumor growth by blocking the binding of tumor cell surface CD44 to hyaluronic acid. Thus, this work teaches a hyaluronic acid binding dependent mechanism for the CD44 effect directly on melanoma tumor cell growth.
Alpaugh et al. (Exp. Cell Res. 261, 150-158 (2000)) discloses myoepithelial-specific CD44 and its antiangiogenic properties. This study deals with HA-binding properties of CD44.
Bajorath (PROTEINS: Structure, Function, and Genetics 39: 103-111 (2000)) discloses CD44 and its binding to HA, cell adhesion and CD44-signalling. Moreover, CD44 mutagenesis experiments are disclosed involving among others the well-established non-HA-binding mutations R41A and R78S, and their impact on CD44-binding to HA.
Bartolazzi et al. (1994) discloses an experiment where mammalian cell expressed CD44HRg-molecule inhibits tumor growth in nude mice. A mutant molecule CD44-R41A-Rg, not mediating cell attachment to hyaluronate, also expressed from mammalian cell did not have similar effect.
Thus, the prior art discloses the potential use of CD44 to specify that any effects are dependent on HA-CD44-interaction. Consequently, all utility ascribed this far to CD44-derived peptides is directly dependent on their ability to bind hyaluronic acid.
Given that hyaluronic acid is widely expressed in the body at high levels, a treatment based on inhibition of this extracellular component result in a high risk for unwanted side effects outside of the tumor. Furthermore, because of the high total amounts of HA in the body, such strategy will require high doses of HA-blocking recombinant proteins, thus even further increasing the risk for side effects.
Accordingly, a need exists for finding novel drugs for treating tumors, as well as novel pathways for the relation between CD44 and tumor growth, in order to provide new drug targets, which avoid the side effects described above.
There is also a clear need for a drug that could be administered in substantially smaller doses than substances having primary effect on CD44-HA binding function.
In addition, there is a need to develop novel inhibitors of angiogenesis, as these constitute potential medicaments not only for cancer, but also for an array of common diseases as disclosed above. To this end, it is important to elucidate the relation between CD44 and angiogenesis, in particular the potential direct effects of CD44 on the vasculature and on the various diseases that are dependent on new blood vessel formation.